基于弹塑性小孔扩张理论的隧-土-桩相互作用与变形控制研究

With the three-dimensional development of urban underground space, problems related to interaction between tunnels and adjacent structure have become increasingly highlighted in underground approaching construction. This project aims to resolve the problem of tunneling under existing piles, based on new methods with cavity expansion theory in geomaterials and large-scale physical modelling of soil-structure interaction. The study examines the effects on both pile bearing capacity and settlement induced by tunnelling operation, an eventually investigates the mechanisms of tunnel-soil-pile interactions. By adopting the unified clay and sand model and the large-strain assumptions, rigorous cavity expansion and contraction solutions are derived for an arbitrary cavity under various drainage conditions, which could provide the stress-strain distributions and developments of surrounding soil. A tunnel-pile interaction model is then established based on the proposed solutions, to evaluate the degradation of pile bearing capacity, mobilised safety factor and pile settlement for a given tunnel volume loss. In association with experimental data from large-scale physical modelling, pile bearing capacity degradation and settlement are obtained during whole tunnelling process, providing the accurate predictions of deformations in underground approaching construction, which indicate the mechanisms of tunnel-soil-pile interaction. Eventually, bearing capacity criterion, safety factor criterion and deformation control criterion are therefore proposed in terms of the tunnel-soil-pile system, contributing to the soil deformation control and the influence on adjacent structures in tunnel engineering.

随着城市地下空间的立体式发展，“地下近接工程”中隧道与邻近结构相互作用问题日益突显。本项目拟针对隧道下穿桩基问题，采用岩土介质小孔扩张理论和土与结构相互作用大尺度三向加载模型试验的新方法，开展隧道掘进对既有桩基承载力和沉降影响研究，探索隧道与邻近桩基相互作用的力学机理。基于统一砂黏土本构模型和大应变假设，获得任意小孔在不同排水条件下扩张和收缩的弹塑性解析解，进而分析孔周土体应力应变分布与演化规律；通过该理论建立隧道与桩基相互作用力学模型，提出由地层损失引起的邻近桩基承载力衰减、安全系数折减以及沉降预测方法。结合大尺度三向加载模型试验揭示隧-土-桩相互作用机理，获得隧道开挖全过程对邻近既有桩基的承载力和沉降影响，解决目前地下近接工程变形难以预测的难题；提出隧-土-桩体系的桩基承载力控制准则、安全系数控制准则和变形控制准则，为隧道工程中精细控制土体变形对周围地下结构的影响提供理论依据。

隧道工程及地下管廊的建设过程中必然会涉及到诸多“穿越工程”或“近接工程”，它们不仅在周围土体形成应力松弛和变形，还将不可避免地造成周围桩基沉降、变形甚至失效，影响邻近构筑物的安全可靠性和整体稳定性。本项目针对隧道下穿既有桩基问题，开展了基于弹塑性小孔扩张理论的隧-土-桩相互作用与变形控制的系统研究。首先，获得了基于弹塑性本构模型的小孔扩张应力应变分布及演化规律，提出的一系列弹塑性解析方法，并进行了孔扩张理论在桩基承载力和沉降预测的应用研究以及孔收缩理论在隧道开挖引起土体应力释放及变形的应用研究。其次，基于徐州轨道交通盾构隧道施工区间，通过室内大尺度模型试验和自行设计的微型非接触式位移测量系统，研究了隧道开挖过程中围土卸载变形时空分布规律；使用ABAQUS有限元分析软件针对隧道开挖全过程对邻近桩基的岩土穿越工程进行了三维有限元模拟，研究了隧道穿越桩基对于桩基的承载力和沉降位移的影响。最后，提出了基于弹塑性孔扩理论的隧道与既有桩基相互作用力学模型；分析了隧道开挖影响下土体应力场、应变场分布，提出了邻近桩基承载力衰减、安全系数折减以及沉降预测方法；分析了隧道开挖全过程对周围土体变形及邻近既有桩基的承载力和沉降影响；研究了隧-土-桩相互作用的力学机制，提出了隧-土-桩体系的变形控制准则及措施，为隧道工程中精细控制土体变形对周围地下结构的影响提供理论依据。